1. Field of Invention
This invention relates to polyurethane foams having improved resistance to scorch, smoldering, and hydrolysis and, in particular, it relates to polyurethane foams incorporating polybrominated higher alkylbenzenes and, optionally, triaryl phosphate flame retardants.
2. Description of Prior Art
Polyurethane foams are used primarily for insulation and cushioning. Since they are thermoset polymers, additives such as flame retardants are generally incorporated during polymerization. Equipment for producing polyurethane foams is generally designed to handle liquids, discouraging the use of solid flame retardant additives.
Traditionally, most flame retardants, although efficient in their function of retarding open flame combustion in a polyurethane foam, promote smolder, thermal degradation (scorch), and hydrolysis. It is essential that one or more of these tendencies be minimized in certain foam types or in certain applications areas.
This is particularly true of polyurethane foam produced from polyester polyols. These polyols tend to degrade under humid conditions and to degrade quickly when thermal decomposition or hydrolysis products of flame retardants are present. It is also true that polyurethane foams for certain applications, such as used in furniture sold in the State of California, need to be resistant to smoldering ignition due to contact with a cigarette or other ignition source. In addition in the case of polyester-based polyurethane foams, hydrolytic stability of additives is another important criterion which must be met.
The problems of scorch, smolder and hydrolysis have been addressed in the art. R. S. Rose and K. A. Hughes (Journal of Fire Retardant Chemistry, 9 155 [1982]) have shown that aromatic bromine compounds such as pentabromodiphenyl oxide tend to resist both scorch and smoldering. Pentabromodiphenyl oxide based flame retardants have gained acceptance as flame retardants for polyurethane foams due in part to the relative stability of aromatically bound bromine and its resistance to thermal and hydrolytic degradation. Although pentabromodiphenyl oxide is thus used, its high viscosity, its tendency to solidify with time, and its unknown decomposition products have limited its use.
Aromatic phosphate esters have been used for some time in conjunction with brominated diphenyl oxides as diluents and/or auxiliary flame retardants. However, these compounds are not as effective as halogen-containing flame retardants.
Underwood, et al. U. S. Pat. No. 3,850,882 discloses a three-component flame retardant additive system for polyolefins, especially polypropylene, consisting of
(a) a halogenated alkylbenzene of the formula ##STR1## where X may be Cl or Br: and Y is a hydrocarbon of 1-20 carbon atoms; a is an integer from 0 to 3; and n is an integer from 3 to 6. PA0 (b) stannic oxide: PA0 (c) a bis-phenylalkylene hydrocarbon. PA0 (a) a triarylphosphine oxide or an aryl or alkyl ester of an arylphosphinic acid; PA0 (b) a nuclear brominated alkylbenzene; and PA0 (c) customary auxiliary agents and additives.
The patent does not suggest that such a flame retardant mixture has any utility in polyurethane foams, let alone that the halogenated alkylbenzene would have any such use.
Rueter, et al. U.S. Pat. No. 4,129,551 discloses nonflammable polyester compositions incorporating a phosphorus-containing, multiple component flame retardant additive consisting of:
Polyester compositions based on such agents contain 0.5-10% by weight of bromine and 0.1-2% by weight of phosphorus. Among the nuclear brominated alkylbenzenes described were a compound of the following formula: ##STR2## where x=2 to 5, y and z each are zero or an integer from 1 to 17 and sum of y+z is an integer between 7 and 17.
Mixtures of such agents are also suggested. There is no disclosure that the additive mixture has any utility in polyurethane foams or that the nuclear brominated alkylbenzene may be so-used alone for that or any other purpose.
Therefore, it is a principal object of this invention to provide flame retardant polyurethane foam compositions that do not exhibit scorching or smoldering problems and that exhibit increased hydrolytic stability.
Another objective of this invention is to provide polyether and polyester type polyurethane foams incorporating a superior flame retardant agent.
Yet a further object is to utilize polybrominated higher alkylbenzenes as flame retardant additives in polyether and polyester type polyurethane foams compositions.